This invention relates to a modified resin composition containing phenolic hydroxyl group and a curable resin composition thereof. The invention further relates to the epoxy resin composition which is obtained by epoxidation of said modified resin composition containing phenolic hydroxyl group by epihalohydrin and a curable resin composition of said epoxy resin.
In general, an epoxy resin weight components is broadly applied as a component of paint or adhesive and for various uses such as electric fields or civil engineering because of the excellent chemical and physical properties which an epoxy resin composition originally has. However, the required level for the features of epoxy resin composition are becoming higher and higher along with the progress of each field of application. Especially, in the uses of powder coating, molding materials or paints for inside surface coating of a can, the development of a resin whose contents of lower molecular weight is low is expected. For instance, since an epoxy resin powder coating has a good durability for corrosion and has a strong resistance to chemicals, it is practically used as the paint for an inner and an outer surface coating of a steel tube or as the paint for a steel frame coating.
Generally, as an epoxy resin composition, bisphenol A type solid epoxy resin is used and as a hardener, dicyandiamide, acid anhydride aromatic amine, dihydrazide or phenol resin is used. As a phenol resin which is used as the hardener, a novolac type phenol resin, preferably the modified resin which has a phenolic hydroxyl group at both ends can be used. For instance, the composition obtained by a chemical reaction between a bisphenol type epoxy resin composition obtained by reacting bisphenol such as bisphenol A or bisphenol F with epichlorohydrin under the presence of hydroxide of alkali metal and excess bisphenol. As the modified resin which contains phenolic hydroxyl group, xe2x80x9cTH-4100xe2x80x9d produced by THOTO KASEI, EPICURE 171 and 172xe2x80x3 produced by YUKA SHELL EPOXY and XD-8062xe2x80x3 of DOW CHMICAL are currently in the market. The powder coating which uses above mentioned modified resin as a hardener is disclosed, for instance, in Japanese Patent Laid-open publication 54-7473, Japanese Patent Laid-open publication 58-79011, Japanese Patent Laid-open publication 58-113267 and Japanese Patent Laid-open publication 61-12762, and these powder coating are remarkably improved so as to be applied to outer surface of a pipe. However, in these conventional modified resins which contains phenolic hydroxyl group, since from 5 to 20 wt % of bisphenol A used for the reacted remains, and vaporizes at a baking procedure, following two phenomena are pointed out as serious problems. That is, accompanied with the vaporization of bisphenol A, many tiny pin holes are formed on the surface of coated film and the physical properties of coated film is deteriorated, further the inside of a furnace for baking is polluted. Further, there is another problem that, by the vaporization of bisphenol A, the anticipated mixing ratio with epoxy resin is changed and deteriorates the physical properties of a coated film.
In the fields of powder coating and molding materials, conventional bisphenol type solid epoxy resins have a problem of blocking and deteriorate the stability of quality for storing, when a low epoxy equivalent resin is used. To solve the above mentioned problems, an epoxy resin not containing a low molecular component which causes a blocking problem, whose viscosity at molten state is low and has good fluidity has been expected.
As a method to remove low molecular weight component in solid type epoxy resin, for instance, the method to remove low molecular weight component by a molecular distillation is well known. However, even by this method, it is difficult to remove the low molecular weight component whose degree of polymerization (hereafter shortened to n) is bigger than 0, further the problem that the solid epoxy resin is thermally decomposed by high temperature at the procedure of distillation has been pointed out. Furthermore, since it is necessary to repeat a distillation for several times to remove n=0 component completely, this method is not useful for the industrial utilization. In the document of Japanese laid open publication of 61-231018, the method to remove the low molecular weight component by contact with a hydrocarbon solvent such as xylene is reported, however by this method it is difficult to remove n=0 component selectively and components bigger than n=0 are also removed and also the removing effect of n=0 component is not sufficient. In Japanese patent laid open publication 1-230678, the refined bisphenol type epoxy resin from which low molecular weight component i.e., lower than 800, is reduced or removed by contacting high molecular weight epoxy resin having 2000 to 6000 number-average molecular weight with lower alcohol in an affinity solvent is disclosed. This method is suited to a high molecule epoxy resin containing smaller than 2% of n=0 or n=1 lower molecule components, and the removing effect is not complete. The removing of these lower molecule components is not complete, even after 5 times repetition of rinsing procedure by alcohol, and is not a useful method as an industrial use.
From the view point of sanitation, an epoxy resin composition which does not contain low molecular weight composition is expected. In general, for the use of inside surface coating of a can for beverage, an epoxy/phenol type coating, an epoxy/amino resin coating and an epoxy/urea resin coating are used.
However, recently, kinds of beverage to be packed in a can have become more diverse. Green tea, oolong tea and black tea are becoming more popular as a beverage to be packed in a can. Since these kinds of beverage are heat treated by high temperature (retort treatment) after being packed into cans, components of coating are partially dissolved at this procedure and the lasting of flavor of contents is spoiled. As a coating which has good durability to bending at the can production, a polyvinyl-chloride organosol coating is usually used, however this coating has a problem of sanitation caused by monomer and plasticizer residue, and also has an environmental problem caused by chlorine gas generated when the wasted cans are burned. Therefore, a development of epoxy resin coating which has good durability to bending and an excellent feature for lasting of flavor is desired.
The objects of this invention are to provide a modified resin containing phenolic hydroxyl group [A] which does not contain a vaporizing component at a baking procedure and a curable resin composition thereof; a solid epoxy resin [B] which does not contain a low molecular weight component and has a good fluidity and a curable resin composition thereof; and a low molecular weight component free epoxy resin [C] which forms a coating having good durability to bending and an excellent feature for lasting of flavor and a curable resin composition thereof.
The important points of this invention include, a modified phenolic hydroxyl group containing resin having a low free difunctional phenol content comprising a resin [A] of formula (1), said resin having a phenolic hydroxyl group equivalent of from 300 to 1,200 g/eq; and, wherein residues of unreacted difunctional phenol is less than 5% by weight of resin, and a curable composition (a) comprising the modified phenolic hydroxyl group containing resin and an epoxy resin as the necessary components, [a] an epoxy resin which is solid at room temperature [B] and which comprises the product of epoxidizing the modified resin with epihalohydrin, said epoxy resin having an epoxy equivalent in the range of from 450 to 2,500 g/eq and a curable resin composition (b) comprising the solid epoxy resin and a hardener; an epoxy resin [C] which is solid at room temperature comprising the product obtained by the reaction of said solid epoxy resin and difunctional phenol, said product having an epoxy equivalent of from 1,500 to 60,000 g/eq and a number-average molecule weight of from 3,000 to 15,000; and,
an epoxy resin (c) characterized by a potassium permanganate consumption value smaller than 5 mg O/L, whereas said value is measured on extracted water which is prepared by adding, by a ratio of 1 ml water to 5 cm2 area of unreacted dry film having a thickness of about 10 xcexcm and heat treated at 125xc2x0 C. at high pressure for 1 hour in a sealed bottle and curable resin composition comprising said solid epoxy resin and a hardener. 
(in formula (1), X represents a residue of difunctional phenol and n is 0 or a positive integer; and wherein the X""s at different positions may be the same or different)
The modified resin containing phenolic hydroxyl group [A] represented by above mentioned formula (1) can be produced by a direct synthetic method which reacts difunctional phenol with epihalohydrin or by an indirect synthetic method which reacts epoxy resin with difunctional phenol. Said two methods can be preferably used. In a case of the direct synthetic method, the modified resin [A] can be obtained by reacting epichlorohydrin with excessive difunctional phenol in the presence of sodium hydroxide catalyst, then removing unreacted difunctional phenol. Meanwhile, in a case of the indirect synthetic method, the modified resin composition [A] can be obtained by reacting epoxy resin with excessive difunctional phenol, then removing unreacted difunctional phenol residue. The phenolic hydroxyl group equivalent of the modified resin obtained by the direct and indirect synthetic method is desirably in the region of from 300 to 1200 g/eq; further, the residue of difunctional phenol is desirably smaller than 5 wt %. From the industrial view point, since the modified resin whose hydroxyl group equivalent is smaller than 300 g/eq and bigger than 1,200 g/eq is difficult to produce, the desirable region of hydroxyl group equivalent is from 350 to 800 g/eq and is more desirably from 400 to 700 g/eq. If the residue of difunctional phenol is bigger than 5 wt %, the physical property of curable composition is affected, therefore the amount of residue is desirably smaller than 1 wt %, and more desirably smaller than 0.5 wt % and furthermore desirably smaller than 0.1 wt %.
As the difunctional phenol to be used for the synthesis of the modified resin containing phenolic hydroxyl group of this invention, bisphenol A, bisphenol F, bisphenol S, tetrabromobisphenol A, bisphenol AD, bisphenol C, catechol, resorcin, hydroquinone and others can be mentioned. Further, as the difunctional epoxy resin, the epoxy resin epoxidated using at least one kind of these difunctional phenol, hydrogenated bisphenol A, 1,6 hexanediol, diglycidylesters of alcohol such as polypropyleneglycol, hexahydrophthalic acid, diglycidylesters such as dimer acid and others can be mentioned, and especially a bisphenol type epoxy resin is desirably used. As the bisphenol type epoxy resin, a lower molecular weight type which is obtained by a direct synthetic method is desirably used, and especially a liquid epoxy resin of bisphenol A type or bisphenol F type which is on the market as the general liquid type is desirable.
To obtain the modified resin containing phenolic hydroxyl group by the direct synthetic method, excessive difunctional phenol is reacted with epichlorohydrin. A partially epoxidized epoxy resin is obtained which is further reacted with unreacted difunctional phenol to produce the modified phenolic hydroxyl-containing resin. Mole number of difunctional phenol to be added is from 1.2 to 10 mole, desirably from 1.5 to 5 mole to 1 mole of epichlorohydrin. When the mole number of difunctional phenol is smaller than 1.2 mole, the molecular weight of obtained resin becomes too high. When it is bigger than 10 mole, the residue of difunctional phenol become too much to be removed and the commercial production becomes impossible. Further, mole number of sodium hydroxide to be added is from 0.7 to 1.2 mole to 1 mole of epichlorohydrin and is treated as the solution from 8 to 15% concentration by weight. The direct synthetic reaction can be carried out within the limit of temperature from 40 to 120xc2x0 C. for 1 to 8 hours. Furthermore, said reaction can be carried out in a solution which does not react with epoxy group. As the substantial examples of this solution, aromatic hydrocarbons such as toluene, xylene or benzene, ketones such as methylisobutylketone, methylethylketone, cyclohexanone or acetone, glycolethers such as diethyleneglycolmethylether, propyleneglycolmethylether or dipropyleneglycolmethylether, aliphatic ethers such as diethylether, dibutylether or ethylpropylether or alicyclic ethers such as dioxane or tetrahydrofuran can be mentioned.
To obtain the modified resin containing phenolic hydroxyl group by the fusion method, excessive difunctional phenol is reacted with epoxy resin. As in the direct method, mole number of difunctional phenol to be reacted with 1 mole of epoxy resin is from 1.2 to 10 mole, desirably from 1.5 to 5 mole. As the difunctional phenols which are used for the indirect synthetic method, one or more kinds of aforementioned phenol can be used. When the mole number of difunctional phenol is smaller than 1.2 mole, the molecular weight of obtained resin becomes too high and consequently the fluidity of molten stage is deteriorated. When it is bigger than 10 mole, the residue of difunctional phenol become too much to be removed and the commercial production becomes impossible. At the reaction, epoxy resin and difunctional phenol can be put in simultaneously, or epoxy resin can be added slowly into difunctional phenol. Further, the reaction can be carried out under the presence of catalyst within the limit of temperature from 30 to 220xc2x0 C. for 30 minutes to 6 hours, desirably from 80 to 160xc2x0 C. for 1 to 6 hours. As the catalyst, metal hydroxide such as sodium hydroxide or potassium hydroxide, tertially amines such as 2-methylimidazole or 2-ethyl 4-methyl-imidazole, quaternary ammonium salts such as tetramethyl-ammoniumbromide or benzyltrimethylammonium-bromide, phosphines such as triphenylphosphine or tributylphosphine, phosphonium salts such as n-butyltriphenylphosphonium-bromide can be mentioned. The desirable amount of catalyst to be added is from 10 to 10,000 ppm to difunctional phenol used at the reaction. As in the direct method, the reaction can be carried out in a solution, and the point when the epoxy group is vanished is regarded as the end point of the reaction.
After the reaction, as a method to remove the residue of unreacted difunctional phenol, a method by solvent extraction, a method by re-crystallization, a method by molecular distillation, a method by separating film, a removing method by dissolving in alkali aqueous solution and others can be mentioned. From the industrial view point, a molecular distillation or a dissolving method in alkali aqueous solution are preferably used. The removing method by dissolving in alkali aqueous solution is illustrated as follows. After the direct or indirect reaction, aforementioned solution is added by the amount so as the solid portion to be diluted to 20xcx9c50 wt % concentration, then an alkali metal hydroxide is added, reacted with the residue of difunctional phenol and alkali metal phenolate is formed. Molar number of alkali metal hydroxide to be added corresponds to 0.7 to 1.5 mole to 1 mole of phenolic hydroxide group of difunctional phenol which is unreacted with the formed modified resin having phenolic hydroxide group at the end. The reaction is carried out at the temperature of 30xcx9c100xc2x0 C., for 10 minutes to 5 hours. Then, only alkali metal phenolate of difunctional phenol is separated and removed from the high molecular product which is dissolved in the solution. As an alkali metal hydroxide, an aqueous solution of sodium hydroxide or potassium hydroxide whose concentration is smaller than 15 wt %, may be used. When the concentration of aqueous solution is bigger than 15 wt %, difunctional phenol is deposited. The desirable limitation of concentration is from 2 to 13% by weight. Almost whole residue of difunctional phenol can be removed by one separating operation. After the removal of difunctional phenol residue, the product is neutralized by phosphoric acid or sodium phosphate and rinsed by fresh water, and the solvent is distilled out. Thus, the solid modified resin containing phenolic hydroxide group [A] whose phenolic hydroxide equivalent does from 300 to 1200 g/eq and in which difunctional phenol is not substantially is obtained.
The distinctive feature of curable composition of this invention is the use of said modified resin containing phenolic hydroxide group [A] with the epoxy resin as a hardner. As the epoxy resin, there can be used the epoxy resin which contains at least two epoxy groups in a molecule and whose melting point is from 50 to 140xc2x0 C., which is usually used as a powder coating. For example, bisphenols such as bisphenol-A and bisphenol-F, novolac type polyglycidylether such as di-glycidylether, phenolnovolac and cresolnovolac, polyglycidylester of polycarboxylic acid and alicyclic epoxy resin can be mentioned, and one kind or a mixture of these compounds can be used.
As the modified resin containing phenolic hydroxide group [A] which is used as a hardener of the curable composition [a] of this invention the compound whose phenolic hydroxyl equivalent is 30 to 1,200 g/eq is desirable and 400 to 700 g/eq is more desirable. The desirable region of softening temperature is from 50 to 140xc2x0 C. and more desirable region is from 80 to 120xc2x0 C. The desirable region of the amount for use of modified resin containing phenolic hydroxide group is from 0.6 to 1.5 phenolic hydroxyl equivalent, more desirably from 0.6 to 1.0 equivalent to 1 epoxy group equivalent of epoxy resin. Further, as a hardener, acid anhydride or polyamine which are usually applied to a powder coating can be used together with the modified resin ofthis invention, as needed.
To the curable composition [a] of this invention, a color pigment such as titanium oxide or carbon black, an extender such as calcium carbonate or talc, a rust preventive pigment such as zinc powder or aluminum phosphate, a filler material for reinforcement such as glass flakes or glass fiber, cure actuator such as 2-methylimidazole or triethylphosphine, a flow control agent and a dispersing agent which are usually used in a powder coating and an ultraviolet absorber can be added.
The curable composition [a] of this invention can be obtained by melting and mixing an epoxy resin, a modified resin containing phenolic hydroxide group and other additives, as needed at the temperature of 80xcx9c120xc2x0 C., then cooling down and crushing the solidified mixture. As the melting and mixing apparatus, a heating roller, a heating kneader or an extruder can be used. And the powder coating compound of this invention can be coated on the surface of an article by means of an electrostatic painting method, fluidizing-bed coating method or others. The powder coating compound of this invention can be applied to a reinforcement, a steel pipe and a deformed bar. The baking and curing condition of the coated film is 180xcx9c240xc2x0 C. temperature for 1xcx9c30 minutes and the article to be coated can be previously heated before coating.
The modified phenolic hydroxyl group containing resin of this invention [A] can be epoxidated by well known method which epoxidates a resin by epihalohydrin in the presence of alkali metal hydroxide, and a solid epoxy resin [B] which has 450 2500g/eq epoxy equivalent value can be obtained. As the kind of epihalohydrin to be used in this application, epichlorohydrin, epibromohydrin and epiiodohydrin can be mentioned and especially epichlorohydrin can be preferably used. As the alkali metal hydroxide, sodium hydroxide can be preferably used. Excessive amount of epihalohydrin of 2xcx9c30 mole, desirably 10xcx9c20 mole is added to 1 mole of phenolic hydroxide group of material resin, and the amount of alkali metal hydroxide to be used is from 0.7 to 1.1 mole to phenolic hydroxide group equivalent of material. It is desirable to react at the temperature from 40 to 120xc2x0 C. region while removing the generated water.
After the reaction, the excess epihalohydrin is vaporized off, then the reacted product is dissolved into aforementioned solvent, and purifying reaction is made by adding 1 to 50 mole of alkali metal hydroxide to the hydrolytic chlorine of generated epoxy resin. By removing byproduct salt by washing with water or by filtration and removing solvent by vaporization, the epoxy resin [B] which is solid at room temperature whose epoxy equivalent is from 450 to 2,500 g/eq can be obtained. The epoxy resin whose epoxy equivalent is smaller than 450 g/eq has a problem of productivity at the production of solid resin, and the epoxy resin whose epoxy equivalent is bigger than 2,500 g/eq is difficult to remove the solvent after epoxidation.
Since the epoxy resin [B] which is solid at room temperature of this invention does not contain low molecular weight component, and further since the proportion of high molecular weight component can be decreased, the distribution of molecular weight is sharper than that of the epoxy resin in the well known solid epoxy resin. The viscosity of molten state is low and the glass transition temperature of it becomes higher, further it has a good resistance to blocking and has a good fluidity.
The curable composition [b] of this invention is composed at least by said solid epoxy resin [B] and a hardener. As the hardener, conventional hardeners which are used for hardening of an epoxy resin can be used. For instance, amines such as diethylenetriamine, triethylenetriamine, isophoronediamine, methaxylenediamine or diaminodiphenyl-methane, acid anhydride such as phthalic anhydride, hexahydro phthalic anhydride, nadic anhydride and trimellitic anhydride, polyester resin having acid functional end group, aminopolyamide resin which is a condensation product of dimer acid between diethylenetriamine or triethylamine, polysulfido resin which has mercaptan group at the end, boron trifluoride amine complex, novolac resin obtained by condensation reaction between phenols and formalin, any kind of compound which has phenolic hydroxyl group, dicyanidediamide, adipic dihydrazide, organic acid dihydrazide such as sebacic dihydrazide, polyisocyanates, imidazoles, resol phenol resin and amino resin can be mentioned.
To the curable composition [b] of this invention, at least one kind of conventional epoxy resin selected from the group mentioned below can be added at need. That is, for instance, polyglycidylether of bisphenols such as bisphenol A and bisphenol F, polyglycidylether of alcohol such as polyethyleneglycol or polypropyleneglycol, polyglycidylester of hexahydrophthalic acid or dimer acid, polyglycidylamine such as diaminodiphenylmethane and novolak type polyglycidylether such as phenol novolak or cresol novolak can be mentioned. Further, a filler, a diluent or an accelerator can be added at need. The curable composition [b] of this invention can be used for various uses, for instance as a coating such as an anti-corrosive paint, powder coating, PCM paint or canned paint, as a civil engineering and construction industry material, as an adhesive, to an electric and electronics industry component such as an electric insulation (powder type) or a virtual adhesive for semiconductor chip or as a composite such as a laminate (printed circuit board) or a carbon fiber reinforced plastic (CFRP).
By addition polymerization reaction between solid epoxy resin [B] and difunctional phenol, an epoxy resin which is solid at room temperature [C] whose epoxy equivalent is from 450 to 2,500 g/eq and a number-average molecular weight is from 3,000 to 15,000 can be obtained. This solid epoxy resin [C] is an epoxy resin of high molecular weight which does not contain water extractive low molecular weight component. Therefore, a distinctive feature of this resin is that the potassium permanganate consumption value measured on extracted water is smaller than 5 mg O/L. This extracted water is prepared by following procedure; add distilled water to the coated resin film by the proportion of 1 ml of distilled water to 5 cm2 area of unreacted dry film of said uncured resin having 10 m thickness, heated in sealed bottle at the temperature of 125xc2x0 C. for 1 hour, and the obtained extracted water is used for the measurement. Therefore, said solid epoxy resin [C] is suited for the use of an inner surface coating of canned beverage, which requires good hygiene and good maintenance of flavor.
As the difunctional phenol which can be used for addition polymerization, bisphenol A, bisphenol F, bisphenol S, tetrabromobisphenol A, bisphenol AD, bisphenol C, catechol, resorcinol or hydroquinone can be used, and one kind or the mixture of more kinds of these can be used. Among those, bisphenols such as bisphenol A and bisphenol F is desirably used.
Generally, the addition polymerization can be completed in the presence of catalyst by reacting at the temperature of 80xcx9c220xc2x0 C. for from 30 minutes to 20 hours. As the catalyst, same kinds and same amount of catalysts which are used in the case of said modified phenolic hydroxyl group containing resin [A] can be desirably used. That is, alkali metal hydroxides, tertiary amines, imidazoles, quaternary ammonium salts, phosphines or phosphonium salts can be mentioned. At the preparation of solid epoxy resin [C], the reaction can be carried out in the solvent which does not react with epoxy group. As the substantial examples of this solution, aromatic hydrocarbons such as toluene, xylene or benzene, ketones such as methylisobutylketone, methylethylketone, cyclohexanone or acetone, glycolethers such as diethyleneglycolmethylether, propyleneglycolmethylether or dipropyleneglycolmethylether, aliphatic ethers such as diethylether, dibutylether or ethylpropylether or alicyclic ethers such as dioxane or tetrahydrofuran can be mentioned.
Epoxy equivalent of solid epoxy resin [C] of this invention is desirably to be in the region from 1,500 to 60,000 g/eq. When the epoxy equivalent is smaller than 1,500 g/eq, processsbility after being coated is not sufficient and when it is bigger than 60,000 g/eq, the production in industrial scale becomes very difficult. And when the number-average molecular weight is smaller than 3,000, processability after being coated is not sufficient and when it is bigger than 15,000, the production in industrial scale becomes very difficult.
As the hardener component of the curable composition [c] of this invention, generally a substance which is used as a hardener of epoxy resin can be used, especially, resol resin and amino resin are desirable. As the resol resin, for instance, a condensation product of phenols such as phenol, alkyl phenols or bisphenols with aldehydes such as formaldehyde or acetoaldehyde under the presence of basic catalyst and alkyletherficated compound of it with alcohols such as methanol, n-butanol or isobutanol can be mentioned. On the other hand, as the amino resin, a condensation product of urea, melamine or benzoguanamine with formaldehyde in the presence of basic catalyst and alkyletherficated compound of it with alcohols can be mentioned.
At the production of the curable composition [c] of this invention, one kind alone or a mixture of more kinds of these hardener components can be used in accordance with need. And the blending amount of the curable composition [c] is to be within the region from 1 to 50% by weight to the total weight of compound. When the blending ratio of the curable composition [c] is smaller than 1 wt %, the cross linkage of resin is not sufficient and a retort resistance of coated film is not good, and when it is bigger than 50 wt %, the processing and bending feature of it are not good. The curable composition [c] of this invention can be used without solvent or by dissolving it in solvent at need. Any kind of solvent which can dissolve the composition homogeneously can be used.
The curing composition [c] of this invention can be used as the water soluble paint, by dispersing said solid epoxy resin [C] in water by well known method, for example, a method to partially esterify it with the acrylic resin which has carboxylic group in the presence of esterifying catalyst, or a method to copolymerize with unsaturated monomer which has carboxylic group in the presence of free radical generating agent.
The curable composition [c] of this invention can be used together with a reaction accelerating agent at need, for example, a curing catalyst such as phosphoric acid or paratoluenesulfonic acid. Further, in curable composition [c] of this invention, various additives which are usually used in epoxy resin coating such as a filler, a reinforcing agent, a pigment or fluid controlling agent can be added at need.
As the method to coat the curable composition [c] of this invention, the well known method such as a spray method, a roll coating method, a method by brush or a method by pouring can be mentioned. In general, the curable composition [c] of this invention is baked at the temperature from 120 to 300xc2x0 C. for 30 seconds to 20 minutes and the coated film can be obtained.